Methods : After written consent is obtained, the surgeon inserts, at the end of surgery, a multiholes catheter under muscular layers. Patients are randomised in two groups : The "treated group" receives ropivacaine 0.2% infusion (bolus of 10 milliliters (mL) followed by 8 mL/h continuous infusion during 48 hours) and the "control group" receives saline solution (0.9%). In addition, all patients receive patient-controlled intra-venous morphine analgesia. The investigators hypothesize that the "treated group" will consume morphine less than the "control group".